Petrogenesis of Hawaiian Lavas: Investigations Using Radiogenic and Non-Traditional Stable Isotopes

Earth’s mantle is the most voluminous part of the planet and is inaccessible to direct investigations. It is only possible to study it through indirect methods, such as the chemical makeup of erupted lavas. The Hawaiian Islands are thought to be the product of the mantle plume hypothesis, sometimes called a hot spot. Material from the Earth’s mantle is brought to the surface and erupted as magnesium rich lavas and form basalts. Hawaii is the longest lived active hot spot on Earth and makes it an ideal candidate for understanding the evolution of the Earth’s mantle and how lavas cool and crystallize. To that end, the Hawaii Scientific Drilling Project (HSDP) drilled and recovered over 3 km of basalts from Mauna Kea Volcano, Hawaii, to understand the evolution of a mantle plume volcano. This project investigates the different geochemical end-members that contribute to the shield stage of Mauna Kea Volcano, Hawaii, by analyzing the major and trace element compositions, as well as the radiogenic isotope (Sr-Nd-Hf-Pb) ratios of a unique series of shield stage basalts from HSDP called the high-CaO basalts. Their trace element concentrations are like that of rejuvenated stage basalts and their radiogenic isotope ratios fall within the range of rejuvenated stage basalts. I connect the high-CaO basalts to rejuvenated stage basalts through radiogenic isotope data and trace element modeling. In chapter 2, I show that the geochemical makeup of high-CaO basalts can be produced by melting a rejuvenated stage source to higher degrees. This suggests the same mantle source that produced rejuvenated lavas could have produced the high-CaO basalts, and that a depleted mantle component is intrinsic to the Hawaiian mantle plume that builds the shield stage. Kilauea Volcano on the island of Hawaii is the most active volcano on Earth and is currently erupting. It has been continuously sampled since its 1983 summit eruptions and allows us the rare opportunity to understand the real-time geochemical evolution of a volcano. Joint scientific ventures in the 2000s between the United States Geologic Survey and the Japan Marine Science and Technology Center, recovered by submersible submarine samples of Kilauea. Published age data show that some of the recovered submarine samples represent preshield ages, making Kilauea the only Hawaiian volcano that has both preshield and shield stage samples for study. In chapter 3, I show through new partial melting models that anomalous preshield Kilauea samples can be produced by low degree partial melts of a phlogopite-bearing source, and their sources have trace element patterns similar to that of high-CaO sources and could be the product of the same depleted end-member, meaning the depleted component universal in the mantle plume. The field of geochemistry has made leaps and bounds in the last two decades, particularly with the advent of multi-collector inductively coupled plasma mass spectrometers (MC-ICP-MS) that is capable of high precision stable isotope analysis. Magnesium is a major element and important geochemical parameter in monitoring the crystallization history of mafic lavas. Initial studies of magnesium isotopes showed no measurable variation in 26Mg. In chapter 4, I focus on lavas from Mauna Kea Volcano that transition from the tholeiitic shield stage to the more evolved, alkalic post-shield stage to monitor the effect of enhanced fractional crystallization. I present new 26Mg data for shield and postshield Mauna Kea lavas, in combination with thermodynamic MELTS models that show crystallization of oxide mineral phases can have fractionate stable isotopes of magnesium and can be used to detect the formation of these phases

Potential Mercurian Analogues: Aubrite and Enstatite Chondrite Impact Melt Meteorites

The MESSENGER (MErcury Surface Space ENvironment GEochemistry and Ranging Spacecraft) mission provided new data that have helped us better constrain the surficial mineralogy and composition of Mercury. Mercury has an extremely low oxygen fugacity (f O2) (Iron Wustite (IW) -7.3 to IW -2.6), and at these unique conditions, elements, which usually exhibit lithophile behavior on Earth, can exhibit chalcophile or siderophile behavior on Mercury. No samples have been returned from Mercury; therefore, we must study candidate meteorite analogs to better understand the formation conditions of minerals inferred to be present at the Mercurian surface and Mercurian magmatic processes. In this study, we present a comprehensive analysis of a representative suite of eight aubrites and four enstatite chondrite impact melts (ECIM), which both have a similar f O2 to Mercury, and contain exotic sulfides that have been inferred to be present at the Mercurian surface. These characteristics allow us to assess their relevance for understanding the mineralogy and magmatic processes of Mercury. The ECIM were previously classified as aubrites, but we show that they are actually ECIM with a potential EH (high enstatite) parent body origin due to the presence of niningerite, Si-enriched kamacite, and uniform Ni in schreibersite. We propose that, with respect to the aubrites, the ECIM represent an ideal candidate for Mercurian studies due to their mineralogy and modal mineralogy. Compared to the aubrites, the ECIM samples do not contain forsterite or diopside, show a poorer sulfide diversity, contain graphite, and have a higher volume percentage of metal phases. Although the Mercurian surface contains forsterite and diopside, graphite and a similar amount of metal and sulfides as seen in the ECIM are inferred to be present on Mercury. According to the calculated normative Mercurian mineralogy, both candidate meteorites are most analogous to the Caloris Basin and Northern Plains Lower Mg regions

A New Look at Aubrites: Investigating 3D Modal Mineralogy with X-Ray Computed Tomography

The aubrites (approximately 30 known meteorites) are a unique group of differentiated meteorites that formed on asteroids with oxygen fugacities (O2) from approximately 2 to approximately 6 log units below the iron-wustite buffer. At these highly reduced conditions, elements deviate from the geochemical behavior exhibited at terrestrial O2, forming FeO-poor silicates and exotic sulfides. While previous studies have described the petrology and 2D modal abundances of aubrites, this work investigates the 3D modal mineralogies of silicate, metal, and sulfide phases in aubrite samples, which are then compared to the available 2D data. In addition to 3D modal mineralogies, we have examined the geochemistry of fourteen aubrites, including mineral major-element compositions, bulk-rock compositions, and oxygen isotopic compositions to understand their formation and evolution at extreme O2 conditions. We utilize X-ray computed tomography (XCT) to non-destructively analyze the distribution and abundances of mineral phases in aubrites and locate composite clasts of sulfide grains for future analytical study. In order to better constrain elemental behavior under reduced conditions, we specifically target minerals phases that comprise moderately volatile elements (i.e. oldhamite [CaS], caswellsilverite [NaCrS2] and djerfisherite [K6Na(Fe,Cu,Ni)25S26Cl]) as it has been shown that their geochemical behavior changes as a function of O2. Currently, we have produced 3D scans of the Norton County aubrite. The results of the XCT data have allowed for the determination of the abundances of silicate groundmass (i.e., enstatite, forsterite, albite, and diopside), light (based on electron density) sulfides (i.e. alabandite [MnS] and daubrelite [FeCr2S4]), heavy (based on electron density) sulfides (i.e., troilite [FeS]), and Fe,Ni metal by segmenting a density histogram in Volume Graphics Studio software. XCT scans of additional aubrites are underway. By combining the 3D representation of the exotic phases found in aubrites with existing 2D characterizations, we are able to better determine modal abundances. By integrating 3D and 2D modal abundances and geochemistry, we can ultimately better constrain aubrite petrogenesis and elemental partitioning under reduced conditions. Furthermore, application of this new 3D approach offers the opportunity to identify and select clasts for future study prior to cutting the sample, which will minimize sample loss of this precious material

Use of temperature to improve West Nile virus forecasts

Ecological and laboratory studies have demonstrated that temperature modulates West Nile virus (WNV) transmission dynamics and spillover infection to humans. Here we explore whether inclusion of temperature forcing in a model depicting WNV transmission improves WNV forecast accuracy relative to a baseline model depicting WNV transmission without temperature forcing. Both models are optimized using a data assimilation method and two observed data streams: mosquito infection rates and reported human WNV cases. Each coupled model-inference framework is then used to generate retrospective ensemble forecasts of WNV for 110 outbreak years from among 12 geographically diverse United States counties. The temperature-forced model improves forecast accuracy for much of the outbreak season. From the end of July until the beginning of October, a timespan during which 70% of human cases are reported, the temperature-forced model generated forecasts of the total number of human cases over the next 3 weeks, total number of human cases over the season, the week with the highest percentage of infectious mosquitoes, and the peak percentage of infectious mosquitoes that on average increased absolute forecast accuracy 5%, 10%, 12%, and 6%, respectively, over the non-temperature forced baseline model. These results indicate that use of temperature forcing improves WNV forecast accuracy and provide further evidence that temperature influences rates of WNV transmission. The findings provide a foundation for implementation of a statistically rigorous system for real-time forecast of seasonal WNV outbreaks and their use as a quantitative decision support tool for public health officials and mosquito control programs

A proposed framework for the development and qualitative evaluation of West Nile virus models and their application to local public health decision-making

West Nile virus(WNV) is a globally distributed mosquito-borne virus of great public health concern. The number of WNV human cases and mosquito infection patterns vary in space and time. Many statistical models have been developed to understand and predict WNV geographic and temporal dynamics. However, these modeling efforts have been disjointed with little model comparison and inconsistent validation. In this paper, we describe a framework to unify and standardize WNV modeling efforts nationwide. WNV risk, detection, or warning models for this review were solicited from active research groups working in different regions of the United States. A total of 13 models were selected and described. The spatial and temporal scales of each model were compared to guide the timing and the locations for mosquito and virus surveillance, to support mosquito vector control decisions, and to assist in conducting public health outreach campaigns at multiple scales of decision-making. Our overarching goal is to bridge the existing gap between model development, which is usually conducted as an academic exercise, and practical model applications, which occur at state, tribal, local, or territorial public health and mosquito control agency levels. The proposed model assessment and comparison framework helps clarify the value of individual models for decision-making and identifies the appropriate temporal and spatial scope of each model. This qualitative evaluation clearly identifies gaps in linking models to applied decisions and sets the stage for a quantitative comparison of models. Specifically, whereas many coarse-grained models (county resolution or greater) have been developed, the greatest need is for fine-grained, short-term planning models (m–km, days–weeks) that remain scarce. We further recommend quantifying the value of information for each decision to identify decisions that would benefit most from model input

The effects of highly reduced magmatism revealed through aubrites

Enstatite-rich meteorites, including the aubrites, formed under conditions of very low oxygen fugacity (ƒO2: iron-wüstite buffer −2 to −6) and thus offer the ability to study reduced magmatism present on multiple bodies in our solar system. Elemental partitioning among metals, sulfides, and silicates is poorly constrained at low ƒO2; however, studies of enstatite-rich meteorites may yield empirical evidence of the effects of low ƒO2 on elemental behavior. This work presents comprehensive petrologic and oxygen isotopic studies of 14 aubrites, including four meteorites that have not been previously investigated in detail. The aubrites exhibit a variety of textures and mineralogy, and their elemental zoning patterns point to slow cooling histories for all 14 samples. Oxygen isotope analyses suggest that the aubrite parent bodies may be more heterogeneous than originally reported or may have experienced incomplete magmatic differentiation. Contrary to the other classified aubrites and based on textural and mineralogical observations, we suggest that the Northwest Africa 8396 meteorite shows an affinity for an enstatite chondrite parentage. By measuring major elemental compositions of silicates, sulfides, and metals, we calculate new metal–silicate, sulfide–silicate, and sulfide–metal partition coefficients for aubrites that are applicable to igneous systems at low ƒO2. The geochemical behavior of elements in aubrites, as determined using partition coefficients, is similar to the geochemical behavior of elements determined experimentally for magmatic systems on Mercury. Enstatite-rich meteorites, including aubrites, represent valuable natural petrologic analogues to Mercury and their study could further our understanding of reduced magmatism in our solar system.12 month embargo; first published: 14 May 2022This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Example forecasts of infectious mosquitoes and human WNV cases for Suffolk County, NY during 2010.

<p>Blue represents the baseline model and red represents the temperature-forced model. The dotted lines are the ensemble mean forecasts and solid lines are the ensemble mean posterior distribution, orange <i>x</i>’s are data points assimilated into the model, orange * are future observations, and the green lines represent the target range of an accurate forecast. A forecast was deemed accurate if: 1) peak timing was within ±1 week of the observed peak of infectious mosquitoes; 2) peak infection rate was within ±25% of the observed peak infection rate; and 3) human WNV cases were within ±25% of the total number of reported cases.</p

The fraction of forecasts accurate for both the temperature-forced model (red) and baseline model (blue) as a function of week of the year for the metrics human WNV cases, peak timing (week of peak mosquito infection rates), peak infection rate, and total infectious mosquitoes.

<p>A forecast was deemed accurate if: 1) peak timing was within ±1 week of the observed peak of infectious mosquitoes; 2) peak infection rate was within ±25% of the observed peak infection rate; 3) total infectious mosquitoes were within ±25% of the observed; and 4) human WNV cases were within ±25% or ±1 case of the total number of reported cases, whichever was larger.</p